The population of Iran has increased on average one million people annually since the first census in 1956. However，the speed of the increase differentiates among periods. There was a baby boom about the 1980s，and the increase of the population slowed down gradually because of the Family Planning policy. In the 21 century，Iran became the first Islamic country with low TFR and low natural population growth rate. Predicted by population experts，the country might face the issue of population decline and the aging problem in 30 to 40 years. Concerned about that，Ayatollah Ali Khamenei，the religious leader，in 2012 publicly criticized the Family Planning policy imposed by the government and decreed the instruction of increasing population in 2014，which was the official turning point from controlling to the encouragement of child birth. Since the 1960s，the Iranian government has adjusted the population policy several times based on the development of population. Except for the 10 years after the Islamic Revolution，the policy has been supportive on the increase and has made prominent achievement. The implementation of Family planning policy is just an external factor to the success of population control in Iran，and it is the development of the society，economy and culture in Iran and the improvement of people’s lifestyle that stand for the decisive factor in the slowing of population increase. Therefore，although there are some legislations and measurements encouraging the increase of population，the whole trend of population development would not have fundamental reverse in a short while.